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Thread: Crack in gunite, water seeping from underneath

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    Crack in gunite, water seeping from underneath

    Our pool developed a large crack and water was leaking about a foot a day. We hired a local pool contractor to renovate it. They chipped out the old plaster and exposed the crack. They patched it with rebar staples every foot or so, then covered it over with concrete. But ground water is still seeping up from the crack, and up through the new concrete. Seems like the water is preventing the new concrete from drying. The contractor says its normal and OK. He said the concrete doesn't need to be sealed and water tight, it's the plaster that does that. Is that true? I'm concerned that if the patch isn't totally solid, it may crack again in the future. I definitely don't want to have to do this job again! Hopefully I'm just being overly paranoid. Any words of reassurance (or concern!) from pool pros? Thanks!

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    Mod Squad jblizzle's Avatar
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    Re: Crack in gunite, water seeping from underneath

    Welcome to TFP!!!

    It is true that the plaster is what makes the pool water tight. But, your concern over the crack opening up again is valid. Hopefully the contractor knew what he was doing and got the crack stabilized and filled in.
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    DaninFLA's Avatar
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    Re: Crack in gunite, water seeping from underneath

    concrete doesn't dry, it cures. it is fine to be submerged in water, and is actually preferable. that's not the issue.

    Did the contractor pump anything into the void behind the crack before they added concrete? you gotta fix that before, or you are going to have a void behind the concrete and when you fill the pool with water there is a good chance the pressure will cause the concrete to flex and the plaster is going to crack, opening up a path for water.

    you can either fill the void with flowable fill, or they could have excavated behind the structure and added compacted fill or stone. not sure how big your pool is, but 1 foot of water a day is a pretty substantial amount of water and could have create some bad scouring/soil removal.

    the fact that your structure cracked in the first place leads me to believe there is a structural issue behind/below the pool. I really hope your contractor properly explored and determined the cause of the crack and just didn't patch it and move on. you got to identify the problem before you come up with a solution.
    Dan
    9,000 gallon in-ground Saltwater pool, plaster, cartridge filer, 1.0 hp pump, Hayward T-15 SWCG, TF-100
    Pool School - Chlorine / CYA Chart; Pool School - Test Kits Compared;

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    Re: Crack in gunite, water seeping from underneath

    Thanks Jason and Dan! Now I'm more worried. The contractor did nothing to shore up behind the crack. They didn't even drill in to see what's behind the crack.

    I'll definitely need to have a chat with these guys. Since they already did the staple patches, is it possible they could just drill some new holes to pump in some fill material? What would be a proper flowable fill? Just more concrete?

    Thanks again for the invaluable info!

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    DaninFLA's Avatar
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    Re: Crack in gunite, water seeping from underneath

    Quote Originally Posted by morgan321 View Post
    Thanks Jason and Dan! Now I'm more worried. The contractor did nothing to shore up behind the crack. They didn't even drill in to see what's behind the crack.

    I'll definitely need to have a chat with these guys. Since they already did the staple patches, is it possible they could just drill some new holes to pump in some fill material? What would be a proper flowable fill? Just more concrete?

    Thanks again for the invaluable info!
    that's concerning that they didn't try to determine the cause. is the crack of the walls of the pool? is there decking that would prevent you from excavating behind the wall to see the issue? they definetly need to see whats behind the wall. you need to have soil behind the wall to support the concrete. who did you hire? was it a pool builder or just a pool refinisher? a pool builder would have the knowledge and tools to evaluate this, but someone that just refinishes pools most likely would not.

    flowable fill is basically just concrete with smaller aggregate and a looser consistency that can be easily pumped into areas. not as strong as typical concrete, but useful for situations like these. its used a lot in construction

    just think how much gutter downspouts can erode bare soil during a big rain event...but we are talking about more water than that over a certain amount of time under your pool. if its been like that for a while, im guessing you have a void behind there. crack probably started off small. once enough water flowed thru it to remove soil the concrete stressed and a larger crack formed.
    Dan
    9,000 gallon in-ground Saltwater pool, plaster, cartridge filer, 1.0 hp pump, Hayward T-15 SWCG, TF-100
    Pool School - Chlorine / CYA Chart; Pool School - Test Kits Compared;

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    Re: Crack in gunite, water seeping from underneath

    The crack starts as a hairline toward the top of the pool and extends vertically down into the base of the deep end. Probably about 12' long total. I think they're probably just a pool refinisher. I actually didn't realize there was a difference. I still would've expected they'd know what they were doing! We're having them replace the deck also, so they could excavate down a ways behind the wall crack to take a look. But judging by how water was seeping back into the pool from the bottom of the deep end (not anywhere on the side wall), I think that's where the big leak has been, and probably where the void would be.

    I think it's very likely there's a void down there. It's a really old pool, probably built in the '60's or so. The crack, has been there probably 6 or 8 years at least. But water would leak only intermittently after long periods of rain. After the ground dried in about a week or so, the leak would always stop. But back in December we had a period very heavy rain, and this time the leak opened wide and never stopped, losing about a foot or so a day.

    I talked the contractor into cutting a 4"-5" hole in the bottom to take a look, and pour in some filler if need be. We'll see how it goes!

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    DaninFLA's Avatar
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    Re: Crack in gunite, water seeping from underneath

    that's good news that the deck is being replaced. I would definitely dig down to take a look, and would be the best way to correct a problem if there is one. it would be just be a matter of backfilling with soil or stone. plus you could also make repairs to the crack from the outside as well. i would do this rather than have them drill a hole in the concrete to examine. doing that just creates a new weak spot in the structure, and i would only suggest that if it was the only option....but deck is getting removed so do it then.

    how wide did the crack open up? did it stay a hairline?

    your description sounds to me like there is going to be a void behind there.

    you got a good game plan it sounds like. keep us updated!
    Dan
    9,000 gallon in-ground Saltwater pool, plaster, cartridge filer, 1.0 hp pump, Hayward T-15 SWCG, TF-100
    Pool School - Chlorine / CYA Chart; Pool School - Test Kits Compared;

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